1. Field of the Invention
This invention relates to one general field of extraction of high molecular weight DNA from test samples, particularly from human whole blood.
2. Background Information
Within the field of medical diagnostics there is a growing new methodology that uses DNA as the material for diagnostic tests.
For this type of diagnostic testing to be commercially competitive, overall cost of DNA based tests have to be minimized. One way of achieving lower costs is to reduce man-hours consumed by the various procedures comprising both extraction of DNA from samples and testing and analysis of DNA; in particular, by improving the efficiency of these procedures by incorporating some level of automation.
It will be appreciated, of course, that a variety of testing procedures have been developed. However, some of these that have been described in the art are based on the ability to obtain the DNA in reasonable volume. For example, referring to U.S. Pat. No. 4,391,688 to Hamelin, there is disclosed an electrophoresis system for multiple agarose slab gels. That system involves adding a solution of a mixture of molecules of mixed molecular weights, such as DNA, to wells formed in a horizontal slab gel, after which the gel is treated by electrophoresis to produce localized bands, each being characteristic of a specific molecular weight.
The method or system described in U.S. Pat. No. 4,391,688 is dependent on having a sufficient volume and concentration of DNA readily available. However, it is precisely this lack of easy availability of concentrated DNA that presents a significant difficulty to the use of DNA in diagnostic tests. This is because one of the most time-consuming steps is the procedure used to extract DNA from its source.
Accordingly, a fundamental object of the present invention is to reduce the processing times inherent in the operation of extracting the DNA from test samples and particularly in extracting the DNA from human whole blood samples.
A further major object is to permit the imposition of rigorous quality control on a DNA extraction procedure by means of automation. This reduces administrative costs normally associated with a quality control program.
Another object is to minimize the possibility of random processing errors during a DNA extraction procedure.
Yet another object is to provide an apparatus that is relatively uncomplicated and is easily expandable to large volume extractions in a DNA-based medical diagnostics laboratory.
Still another object is to make the extraction apparatus modifiable for the purposes of extracting DNA from material other than human whole blood.
A design feasibility study conducted by the present inventors has established that automation of the conventional extraction procedure could only be achieved in part, because of a number of steps involving the centrifuging of samples. Typically, five or more centrifuging steps are involved with conventional extraction procedures. Additionally, various aqueous phases have to be removed by means of wide-mouthed pipetting and returned to plastic tubes that held the original samples. The point that bears emphasis is that the complete conventional procedure takes about four days.
Accordingly, other major objects of the present invention are to develop a procedure and apparatus that can extract DNA from whole blood without the need for any centrifuging steps and in the final analysis, to reduce the time for extracting the DNA from about four days, in conventional practice, to approximately five hours.
Since extractions of the kind being discussed, i.e. those involving purifying and concentrating DNA from crude mixtures such as human whole blood, are to be performed on a large scale, the probability of human error is increased. Therefore, the terms of reference for the invention are the designing and building of apparatus that will incorporate a unique and inexpensive system of DNA extraction; further, the provision of apparatus that will reduce the probability of human error.
Accordingly, further objects of the present invention are to provide an automatable or semi-automatable system, such that the operations are traceable and recordable, whereby the status of the process can be monitored in time. Also, to reduce the cost such that DNA-based diagnostic testing can be competitive with other types of testing.